The Hyperloop

[Rob Dekker]

Not to burst any bubbles on this Hyperloop concept, but there are a LOT of very basic issues to be resolved, and current tests are not even close to addressing them. Here is a quick overview :



Apart from the fact that it looks like Elon is going cheap, relying on students and universities to solve the problems with his design, the winning pod was a small electric car designed for 1 mile range only and ran much faster outside the tube than in it. Yet the concept and realization is given a free and uncritical pass by the media.

While reality is that we are FAR away from solving even some very basic engineering issues with the concept of Hyperloop itself.

[TerryM]

Airlocks that can draw a vacuum in minutes.

I imagine the station has a short "jet bridge" that connects to the pod after the pod stops.  Unlike a jet bridge used in today's airports, it will form a pressure-tight fitting immediately around the door opening, so that virtually none of the vacuum is affected.  Once tightly connected, any sort of door (that can be airtight) can open in any sort of way, if space is available.

I like your solution, but what do we do about the expansion problem if the pod remains in vacuum even while loading/unloading at the station(s)?
Terry

[Sleepy]

Let me note that thermal expansion and size of the door are just TWO of the many issues with the very concept of Hyperloop design.

Other issues include :

- Airlocks would be needed at start and stop stations. Airlocks that can draw a vacuum in minutes. Has that been tested yet ?
- How do you turn the pods around at start and stop stations ?
- How do you 'split' a Hyperloop track, so trains can go to more than one end station ?
- How do you prevent catastrophic failure of the entire system (killing everyone in any pod in the tube) in the case one pod comes of its tracks and penetrates the tube ?
- What to do if a pod gets stranded off the track in a 600 km long tube, with no way out for the passengers ?
- and so on..

Not even talking about keeping this system all under near vacuum.

People really don't realize that that the hyperloop needs to maintain a 99,9% vacuum in a pressurized atmosphere mainly controlled by mother nature, in space we only keep a small pod sealed and pressurized. That's a huge difference.

I don't know of any tests, yet that would be the first large scale test they would have to do if they ever want to reach at least mach 0.8, IMHO. Personally, I can only compare to HVAC's again, and pros are normally using two stage vacuum pumps there. Amateurs with one stage pumps will have to wait for higher temps if they wish to make a successful installation that (hopefully) will last for decades.

Several factors influence the speed of a high vacuum pump, and thus the time required to attain vacuum and remove all moisture from a refrigerant system. Some of the most important are:
the volume capacity of the system itself
the amount of moisture contained within the system
the ambient temperature present
internal restrictions within the system
external restrictions between the system and the vacuum source
Finally: the size of the pump.

The only factors the service technician controls, are the external restrictions between the system and the vacuum pump. The rest is mother nature.

The higher pressure in a system, will flow toward the vacuum pump until it is reduced or equal to the desired pressure. The speed at which it will flow is controlled by the internal dimensions and length of the connecting line. Laboratory tests show that pumpdown time can be significantly reduced by use of larger diameter hoses. For optimum pumping speed you should then keep access lines as short in length, and as large in diameter, as possible.

When reading your gauge, the location of the vacuum gauge tube will affect the reading. The closer to the vacuum source, the lower the reading. When reading the vacuum created in a refrigerant system, you should isolate the vacuum pump with a good vacuum valve and allow the pressure in the system to equalize before taking a final reading.

It sounds like a piece of cake when scaled up to a 600km tube with 20 ton pods at transonic speeds (HTT Mach1 version), right? 

[TerryM]

Let me note that thermal expansion and size of the door are just TWO of the many issues with the very concept of Hyperloop design.

Other issues include :

- Airlocks would be needed at start and stop stations. Airlocks that can draw a vacuum in minutes. Has that been tested yet ?
- How do you turn the pods around at start and stop stations ?
- How do you 'split' a Hyperloop track, so trains can go to more than one end station ?
- How do you prevent catastrophic failure of the entire system (killing everyone in any pod in the tube) in the case one pod comes of its tracks and penetrates the tube ?
- What to do if a pod gets stranded off the track in a 600 km long tube, with no way out for the passengers ?
- and so on..

Not even talking about keeping this system all under near vacuum.

People really don't realize that that the hyperloop needs to maintain a 99,9% vacuum in a pressurized atmosphere mainly controlled by mother nature, in space we only keep a small pod sealed and pressurized. That's a huge difference.

I don't know of any tests, yet that would be the first large scale test they would have to do if they ever want to reach at least mach 0.8, IMHO. Personally, I can only compare to HVAC's again, and pros are normally using two stage vacuum pumps there. Amateurs with one stage pumps will have to wait for higher temps if they wish to make a successful installation that (hopefully) will last for decades.

Several factors influence the speed of a high vacuum pump, and thus the time required to attain vacuum and remove all moisture from a refrigerant system. Some of the most important are:
the volume capacity of the system itself
the amount of moisture contained within the system
the ambient temperature present
internal restrictions within the system
external restrictions between the system and the vacuum source
Finally: the size of the pump.

The only factors the service technician controls, are the external restrictions between the system and the vacuum pump. The rest is mother nature.

The higher pressure in a system, will flow toward the vacuum pump until it is reduced or equal to the desired pressure. The speed at which it will flow is controlled by the internal dimensions and length of the connecting line. Laboratory tests show that pumpdown time can be significantly reduced by use of larger diameter hoses. For optimum pumping speed you should then keep access lines as short in length, and as large in diameter, as possible.

When reading your gauge, the location of the vacuum gauge tube will affect the reading. The closer to the vacuum source, the lower the reading. When reading the vacuum created in a refrigerant system, you should isolate the vacuum pump with a good vacuum valve and allow the pressure in the system to equalize before taking a final reading.

It sounds like a piece of cake when scaled up to a 600km tube with 20 ton pods at transonic speeds (HTT Mach1 version), right? 

Only critique is that a tech also controls the time that a system is kept in vacuum with the 2 stage pump running. During manufacturing or factory repairs pulling a vacuum overnight is a minimum. This is most often impossible with on site repairs.
If you want a system to last 20/30 years you need to weld or silver solder all joints, remove any schrader valves and caps, replace the capacitor and start relay every 5 years, then cross your fingers.
Terry

[Sleepy]

Only critique is that a tech also controls the time that a system is kept in vacuum with the 2 stage pump running.

No. One of the easy tests one can do while installing is to leave the HVAC with vacuum and the vacuum pump switched off. The gauge must not move at all during that time.

If you want a system to last 20/30 years you need to weld or silver solder all joints, remove any schrader valves and caps, replace the capacitor and start relay every 5 years, then cross your fingers.
Terry

My oldest (in this house) is 14 years and still ok, it's a Toshiba with 20 metres of piping. There are a lot older out there.

[Sigmetnow]

Virgin Hyperloop One built an “airlock” with a door that allows their pod to enter their evacuated tube without needing to repressurize the whole tube.

[Bob Wallace]

- Airlocks would be needed at start and stop stations. Airlocks that can draw a vacuum in minutes. Has that been tested yet ?

A solution is to make the airlock as 'form fitting' as reasonable for the pod.  Reduce the amount of space that has to evacuated as much as possible.  They could use a chamber that is already evacuated to suck out most of the air around the pod very quickly and then pump out the residual.

- How do you turn the pods around at start and stop stations ?

Once clear the airlock the pod becomes a vehicle on wheels.  Drive it to a waiting platform for passenger offloading and loading.  There could be several platforms in a station, all leading to a common airlock to reenter the tube.  Pods could travel a semicircular route or use a turntable to change direction.

[Sigmetnow]

Length of the pod doors is not a problem.  The payload bay doors on the space shuttle were 60 feet (18.3 m) long:

The port and starboard doors are 60 feet long with a combined area of approximately 1,600 square feet. Each door is made up of five segments that are interconnected by circumferential expansion joints. Each door hinges on 13 Inconel 718 external hinges (five shear and eight idlers). The lower half of each hinge attaches to the midfuselage sill longeron. The hinges rotate on bearings with dual rotational surfaces. There are five shear hinges and eight floating hinges. The floating hinges allow fore and aft movement of the door panels for thermal expansion.

https://spaceflight.nasa.gov/shuttle/reference/shutref/structure/baydoors.html

[Sigmetnow]

More on metal expansion joints.  But imagine how aerospace technology would improve these.

http://www.sfpathway.com/metal_and_fabric_expansion_joints_dampers_hvac/metal-expansion-joints/

Edit:
NASA already has....

http://www.usbellows.com/blog/2002/03/01/54-diameter-tied-universal-expansion-joint-for-nasa-space-center/

http://www.flexiderusa.com/1489-2/330_inch_expansion_joint_for_nasa/

[DrTskoul]

More on metal expansion joints.  But imagine how aerospace technology would improve these.

http://www.sfpathway.com/metal_and_fabric_expansion_joints_dampers_hvac/metal-expansion-joints/

Edit:
NASA already has....

http://www.usbellows.com/blog/2002/03/01/54-diameter-tied-universal-expansion-joint-for-nasa-space-center/

http://www.flexiderusa.com/1489-2/330_inch_expansion_joint_for_nasa/

One thing to do them in space , another under 14-15 psi of pressure difference....

[TerryM]

Only critique is that a tech also controls the time that a system is kept in vacuum with the 2 stage pump running.

No. One of the easy tests one can do while installing is to leave the HVAC with vacuum and the vacuum pump switched off. The gauge must not move at all during that time.

If you want a system to last 20/30 years you need to weld or silver solder all joints, remove any schrader valves and caps, replace the capacitor and start relay every 5 years, then cross your fingers.
Terry

My oldest (in this house) is 14 years and still ok, it's a Toshiba with 20 metres of piping. There are a loCt older out there.

Congrats on the 14 yr old heat pump, hopefully without major repairs.


The reason for leaving the vacuum pump on for an extended time is that moisture gets entrapped in the refrigerant oil and needs time to migrate to the surface before being vacuumed up. If you simply bring a system to a deep vacuum you miss many of the tiny gas bubbles that need time to migrate through the viscous fluid.


A/Cs & Heat pumps should last many decades even in desert conditions. Most are ruined by poor maintenance, (lack of oil), (dirty air filters) or bad power/ bad capacitors, not the refrigerant charge.


Was Toshiba the Japanese brand that used all yellow wiring? They worked well enough, but made repairs difficult by not utilizing the standard wiring color codes. Not sure if that was the name, but it started with a "T" and was from Japan. Thet met a lot of resistance from the commercial refrigeration sector over their non standard wiring and may have changed their ways.
Probably OK for the residential market.


Terry

[Rob Dekker]

Length of the pod doors is not a problem.  The payload bay doors on the space shuttle were 60 feet (18.3 m) long

Yes, it can be done. If you have enough money for it.
Also, there is this (from your link) :

Thermal seals on the doors provide a relatively air-tight payload compartment when the doors are closed and latched.

I don't think that relatively air-tight is an option on a Hyperloop pod.

[Rob Dekker]

More on metal expansion joints.  But imagine how aerospace technology would improve these.

Speedy showed earlier in this thread that you would need some 7,500 of these expansion joints on a 600 km track. With a 1,500 cycle lifetime (4 years or so).

[Rob Dekker]

Here is one thought for those who still believe in the Hyperloop system :

MagLev has been around for a long time. It goes fast. Yet it is too expensive to be commercially viable.

So why would you think that adding to MagLev the cost of a tube, and then adding all the complexities of traveling into, through and out of near vacuum would be cheaper than plain MagLev ?

[Sleepy]

Only critique is that a tech also controls the time that a system is kept in vacuum with the 2 stage pump running.

No. One of the easy tests one can do while installing is to leave the HVAC with vacuum and the vacuum pump switched off. The gauge must not move at all during that time.

If you want a system to last 20/30 years you need to weld or silver solder all joints, remove any schrader valves and caps, replace the capacitor and start relay every 5 years, then cross your fingers.
Terry

My oldest (in this house) is 14 years and still ok, it's a Toshiba with 20 metres of piping. There are a loCt older out there.

Congrats on the 14 yr old heat pump, hopefully without major repairs.

Thanks, it's untouched besides having to replace the bearings in the indoor unit thanks to a bad decision by Toshiba to use cheaper Panasonic bearings. I still use an indoor unit from a lot older Toshiba (with the older bearings) together with my air to water heat pump.

The reason for leaving the vacuum pump on for an extended time is that moisture gets entrapped in the refrigerant oil and needs time to migrate to the surface before being vacuumed up. If you simply bring a system to a deep vacuum you miss many of the tiny gas bubbles that need time to migrate through the viscous fluid.

Yes, as described earlier upthread, the main reason to use a vacuum pump is to evaporate the moisture. But if the system is leak free, you will reach the desired vacuum in a couple of minutes, then you keep it running just to evacuate the moisture. That's why I responded like I did earlier to the bold part above. Previous reply was a bit short because I was in a hurry yesterday, sorry.

Was Toshiba the Japanese brand that used all yellow wiring?

Those I've seen here for the last couple of decades all had standard wiring. But I wouldn't be surprised, since the Japanese have had a history of doing things their own way.

@All; also back to the hyperloop (even if the above side track emanates from that) it would be nice if people tried to find and post specifications, data and numbers.
The commercials are just boring.

[Sleepy]

More on metal expansion joints.  But imagine how aerospace technology would improve these.

Speedy showed earlier in this thread that you would need some 7,500 of these expansion joints on a 600 km track. With a 1,500 cycle lifetime (4 years or so).

I'm Sleepy, definitely not Speedy.
Also worth a notice, stainless steel (as in that NASA joint) has a higher temperature expansion coefficient than steel.

There are so many factual errors floating around the hyperloop, one example that I've seen many times now in different articles, in short; 100 pascal equals 200,000 feet.
No, 100Pa are closer to 100,000 feet.

In one article, this header caught my eye, since it was quite funny. 

[Rob Dekker]

I'm Sleepy, definitely not Speedy.

Sorry dude. You do not sound sleepy though 

[Rob Dekker]

Basic question : why would anyone think that taking a MagLev, then adding the cost of a tube, and then adding all the complexities of traveling into, through and out of near vacuum would be cheaper than a plain MagLev ?

[Sigmetnow]

More on metal expansion joints.  But imagine how aerospace technology would improve these.

Speedy showed earlier in this thread that you would need some 7,500 of these expansion joints on a 600 km track. With a 1,500 cycle lifetime (4 years or so).

Those numbers assume currently-available products, made of commercially-available materials, for commercially-profitable purposes. 

Progress requires innovation.

Edit:
The Concorde supersonic plane experienced expansion of about a foot between the passenger cabin and the drop-nose cockpit section.  Yet atmospheric pressure was maintained.

Owing to air compression in front of the plane as it travelled at supersonic speed, the fuselage heated up and expanded by as much as 300 mm (almost 1 ft). The most obvious manifestation of this was a gap that opened up on the flight deck between the flight engineer's console and the bulkhead. On some aircraft that conducted a retiring supersonic flight, the flight engineers placed their caps in this expanded gap, wedging the cap when it shrank again.

https://en.m.wikipedia.org/wiki/Concorde

[Rob Dekker]

Apart from the insane technological challenges of traveling a spacecraft through a tube at nearly the speed of sound, and the apparently insurmountable economical challenges of making this system operate below the cost of plain old MagLev or HSR, there is the issue of catastrophic failures.

So let us say that a terrorist places a bit of C-4 explosive on the outside of the tube, and detonates it. It blows a hole in the tube.
At that point, air will be rushing into the tube, and if you are in a pod inside the tube, a wall of air traveling at the speed of sound will come towards you with a pressure of 10 tons/m².
If the immediate impact of that does not kill you right away, your pod will reverse course and travel backwards, crashing into the next pod behind you, causing almost certainly another breach of the tube. The process continues until the entire system catastrophically fails, and everyone in the tube dies.

This inherent susceptibility to catastrophic system failure is another reason why Hyperloop is a REALLY BAD idea.

[Sleepy]

More on metal expansion joints.  But imagine how aerospace technology would improve these.

Speedy showed earlier in this thread that you would need some 7,500 of these expansion joints on a 600 km track. With a 1,500 cycle lifetime (4 years or so).

Those numbers assume currently-available products, made of commercially-available materials, for commercially-profitable purposes. 

Progress requires innovation.

As described earlier, they assume low estimates of the presented solution for the tube, steel.
Numbers will be a lot higher in reality, for tubes built above ground in steel.

The only innovation I've seen is Vibranium for the pods, but this comment got zero comments and I also failed to find specifications, or any data for it:
https://forum.arctic-sea-ice.net/index.php/topic,1094.msg140254.html#msg140254

The Concorde supersonic plane experienced expansion of about a foot between the passenger cabin and the drop-nose cockpit section.  Yet atmospheric pressure was maintained.

Yes, a pressurized small pod at 600,000 microns, in a low pressure environment that never went below ~60,000 microns. 

That is far from a 600km steel tube with 750 microns in a high pressure environment of 750,000 microns, with a pressurized pod inside travelling at transonic speed.

Finally, a quote from you link:

At Concorde's altitude, the air density is very low; a breach of cabin integrity would result in a loss of pressure severe enough that the plastic emergency oxygen masks installed on other passenger jets would not be effective and passengers would soon suffer from hypoxia despite quickly donning them. Concorde was equipped with smaller windows to reduce the rate of loss in the event of a breach, a reserve air supply system to augment cabin air pressure, and a rapid descent procedure to bring the aircraft to a safe altitude.

[Yuha]

Apart from the insane technological challenges of traveling a spacecraft through a tube at nearly the speed of sound, and the apparently insurmountable economical challenges of making this system operate below the cost of plain old MagLev or HSR, there is the issue of catastrophic failures.

So let us say that a terrorist places a bit of C-4 explosive on the outside of the tube, and detonates it. It blows a hole in the tube.

All high speed transportation is susceptible to catastrophic failure. If a terrorist derails a MagLev or HSR train running at full speed, I don't think there will be many survivors.

[Sigmetnow]

Apart from the insane technological challenges of traveling a spacecraft through a tube at nearly the speed of sound, and the apparently insurmountable economical challenges of making this system operate below the cost of plain old MagLev or HSR, there is the issue of catastrophic failures.

So let us say that a terrorist places a bit of C-4 explosive on the outside of the tube, and detonates it. It blows a hole in the tube.

All high speed transportation is susceptible to catastrophic failure. If a terrorist derails a MagLev or HSR train running at full speed, I don't think there will be many survivors.

And compare to flying.  Catastrophic failure at altitude:  the air rushes out, and you fall 30,000 feet. 
Hyperloop tube: air rushes in, and you fall (if at all) ~20 feet.  Hyperloop pod: has oxygen masks, just like aircraft.

[Sleepy]

Oxygen masks like in the Concorde you linked to above?

More on metal expansion joints.  But imagine how aerospace technology would improve these.

Speedy showed earlier in this thread that you would need some 7,500 of these expansion joints on a 600 km track. With a 1,500 cycle lifetime (4 years or so).

Those numbers assume currently-available products, made of commercially-available materials, for commercially-profitable purposes. 

Progress requires innovation.

As described earlier, they assume low estimates of the presented solution for the tube, steel.
Numbers will be a lot higher in reality, for tubes built above ground in steel.

The only innovation I've seen is Vibranium for the pods, but this comment got zero comments and I also failed to find specifications, or any data for it:
https://forum.arctic-sea-ice.net/index.php/topic,1094.msg140254.html#msg140254

The Concorde supersonic plane experienced expansion of about a foot between the passenger cabin and the drop-nose cockpit section.  Yet atmospheric pressure was maintained.

Yes, a pressurized small pod at 600,000 microns, in a low pressure environment that never went below ~60,000 microns. 

That is far from a 600km steel tube with 750 microns in a high pressure environment of 750,000 microns, with a pressurized pod inside travelling at transonic speed.

Finally, a quote from your link:

At Concorde's altitude, the air density is very low; a breach of cabin integrity would result in a loss of pressure severe enough that the plastic emergency oxygen masks installed on other passenger jets would not be effective and passengers would soon suffer from hypoxia despite quickly donning them. Concorde was equipped with smaller windows to reduce the rate of loss in the event of a breach, a reserve air supply system to augment cabin air pressure, and a rapid descent procedure to bring the aircraft to a safe altitude.

This container did just fine, the F4 disintegrated at 700km/h:

[Sigmetnow]

“In the unlikely event of a large scale capsule depressurization, other capsules in the tube would automatically begin emergency braking whilst the Hyperloop tube would undergo rapid re-pressurization along its entire length.”

[Sleepy]

Read that.
I would never use a bomb though, I would just dent it.
This is warm air, that has been cooled off, in that drum.

[Sleepy]

Some other thoughts.

Those airlocks, they will probably have to use several. Maybe one each 2-10 kilometres, along with multiple pressure sensors and vacuum pumps for each section. Airlocks better be open when a pod comes though...

Also insulation of electrical components, thanks to electrical arcing in vacuum. Tesla thought of that once upon a time.

A Vibranium tube, not just the pod.
Carbon fibre is still terribly expensive, but not sensible to thermal expansion. Will also withstand mother nature and other movements, like the forces from the pod itself, better than steel.

It's easier to scrap the hyper and stick with the loop.

[Sigmetnow]

Read that.
I would never use a bomb though, I would just dent it.
This is warm air, that has been cooled off, in that drum.

 I am unable to view your video.

However, the materials and construction of the hyperloop tube, and pod, are hardly comparable to a simple drum.

[Rob Dekker]

Read that.
I would never use a bomb though, I would just dent it.

Since the tube is made of 1 inch thick steel, you probably need a bomb any way to dent it.
But you make an interesting point and potentially even more dangerous than my scenario where the bomb rips the tube open.

Tube wall breach is fairly easy to detect with pressure sensors at regular intervals. So you can alert the pods in the tube (slam on the emergency brake) that there is a massive pressure wave coming their way.
But if the tube wall is only locally dented, or collapsed, there will be hard to detect that until the first pod comes by at full speed crashes into the dented wall. That would rip the pod to shreds and it will cut through the steel wall like a hot knife through butter.

Now we have a severed tube full of debris, which will be blown through the tube on the the wall of air that rushes through the tube at the speed of sound towards the next pod in the tube. That pod will now not just be hit be a shockwave of 10 ton/m² air mass but also by debris traveling at the speed of sound. That debris will shred the second pod too, even if it already came to a halt  after emergency braking. Now we have debris from two pods which will continue to ride the shockwave through the tube, destroying every other pod remaining in the tube.

Man. The more I think about it, this Hyperloop concept is a recipe for massive catastrophic system failure.

[Rob Dekker]

All high speed transportation is susceptible to catastrophic failure. If a terrorist derails a MagLev or HSR train running at full speed, I don't think there will be many survivors.

Here is an overview of HSR accidents :
https://en.wikipedia.org/wiki/List_of_TGV_accidents
As you go through that list, notice that the number of fatalities is limited. Most often there are only some injuries.

That is because HSR does not travel inches away from the inside of a metal tube,  which means that one failure does not lead to imminent death. And HSR does not travel in a vacuum chamber, which means one train failure cannot cause catastrophic failure of the entire system.

[Sleepy]

Read that.
I would never use a bomb though, I would just dent it.
This is warm air, that has been cooled off, in that drum.

 I am unable to view your video.

However, the materials and construction of the hyperloop tube, and pod, are hardly comparable to a simple drum.

The video works fine here, both on my PC and my stupid smart phone.

The material is still steel (apart from HTT's Vibranium pod that noone seems to know anything about) and I would of course use a larger tool, like an excavator or bulldozer.

Piplines are thick:
https://sites.google.com/site/metropolitanforensics/root-causes-and-contributing-factors-of-gas-and-liquid-pipeline-failures

Physical (mechanical) damage (gouges and dents, plain dents, wrinkles, etc. normally created by handling during transportation, construction or maintenance activities or by excavation by utility owners/operators/tenants near the pipelines) - about 11 percent of the incidents.

[Sleepy]

Read that.
I would never use a bomb though, I would just dent it.

Since the tube is made of 1 inch thick steel, you probably need a bomb any way to dent it.
But you make an interesting point and potentially even more dangerous than my scenario where the bomb rips the tube open.

Tube wall breach is fairly easy to detect with pressure sensors at regular intervals. So you can alert the pods in the tube (slam on the emergency brake) that there is a massive pressure wave coming their way.
But if the tube wall is only locally dented, or collapsed, there will be hard to detect that until the first pod comes by at full speed crashes into the dented wall. That would rip the pod to shreds and it will cut through the steel wall like a hot knife through butter.

Now we have a severed tube full of debris, which will be blown through the tube on the the wall of air that rushes through the tube at the speed of sound towards the next pod in the tube. That pod will now not just be hit be a shockwave of 10 ton/m² air mass but also by debris traveling at the speed of sound. That debris will shred the second pod too, even if it already came to a halt  after emergency braking. Now we have debris from two pods which will continue to ride the shockwave through the tube, destroying every other pod remaining in the tube.

Man. The more I think about it, this Hyperloop concept is a recipe for massive catastrophic system failure.

Exactly my point Rob!

Adding another quote from that link I posted in my reply to Sig above.

Between 2004 and 2005, studies performed using metal loss tools reported more than 66,000 dents in 57,000 miles of pipeline, or about 1-2 dents per mile.  Fifty percent of all pipelines contain 10 or more dents. 

[Sleepy]

I was thinking about large scale tunnels with vacuum, why? 
And also about the number of airlocks needed.

It just struck me: LIGO!!
They use 3x2km tubes. And to be fair, they need an air pressure of one-trillionth of an atmosphere, not one thousand of an atm like the hyperloop.
But here's how:
https://www.ligo.caltech.edu/page/vacuum

It took 1100 hours (40 days) of constant pumpdown to evacuate the chambers to their optimal operating pressure. In that time, turbo-pump vacuums removed the bulk of the air in the tubes while the tubes themselves were heated to 150-170 degrees C for 30 days to drive out residual gases.

Maintaining this vacuum requires sophisticated monitors and controls as well as the constant operation of ion pumps that extract molecules outgassing from the tubes and other structures inside the vacuum systems. Stray water molecules are also removed by continuously operating liquid nitrogen cryopumps.

LIGO’s vacuum tubes were constructed of spiral-welded 304L stainless steel a mere 3 mm thick. With its relatively low carbon content, 304L steel is resistant to corrosion, especially at the critical welded seams. Rust did grow on the interior of the vacuum tubes during their manufacture in the 1990’s, so when the tubes were installed at LIGO, the interiors of the tubes were meticulously polished and cleaned to remove rust, significantly reducing the likelihood that oxide flakes will fall through the laser beam or migrate onto optical surfaces, the latter being potentially disastrous to LIGO’s mission.

The 1.2 m diameter beam tubes were created in 19 to 20 m-long segments, rolled into a tube with a continuous spiral weld (far left photo). While a mathematically perfect cylinder will not collapse under pressure, any small imperfection in a real tube would allow it to buckle (a crushed vacuum tube would be catastrophic). To prevent collapse, LIGO's tubes are supported with stiffener rings that provide a significant layer of resistance to buckling under the extreme pressure of the atmosphere. The tubes must withstand these stresses for at least 20 years.

Also found this on the first and most interesting part for the hyperloop:

The first part of this process involves pumping out air from the tube using heavy duty vacuum pumps and reaching a ‘good’ state of vacuum as per the requirements of the project.  The first part is relatively easy and air removal goes smoothly for the first few days.

Turbo Pumps at each end of the tube pumped non-condensable gases, like
hydrogen, while eight Cryo-Pumps were spaced out along the tube to pump the
condensable molecules. This system was closely monitored using about 400
thermocouples. Residual gas molecules in the tube were monitored by a mass
spectrometer throughout the bake. Metal bellows spaced every 130 feet took up the
thermal expansion from the bake and special gauges were used to verify that the
mechanical strains on the tube agreed with the structural modeling.

130 feet or ~40 metres between the thermal joints would mean 15,000 joints on a 600km tube.
Add an airlock and at least 2 pumps for every 2km for a total of 300 airlocks and 600 vacuum pumps. The hyperloop tunnels are larger though.

[sidd]

That spacing is sized for the bake temperature (150C) expansion ...

" Metal bellows spaced every 130 feet took up the thermal expansion from the bake ... "

Ambient T swing will be smaller.

sidd

[Rob Dekker]

Adding another quote from that link I posted in my reply to Sig above.

Between 2004 and 2005, studies performed using metal loss tools reported more than 66,000 dents in 57,000 miles of pipeline, or about 1-2 dents per mile.  Fifty percent of all pipelines contain 10 or more dents. 

Dents in oil and gas pipelines are not always a big deal.
The issue is that the overpressure will want to remove these dents since it pushes outwards.
That is why oil pipelines under high pressure can get away with 1/2 inch thickness pipelines, and still suffer only minor failures (minor being relative, since oil leaks are a huge problem, especially on lines like Keystone XL which carries bitumen, which tend to sink in water and do much more damage to the environment than regular oil. But that is a whole different subject).

Hyperloop on the other hand operates with under-pressure. If a dent appears in the tube, the under-pressure wants to enlarge it. At the count of 10 tons per square meter. Which can easily lead to catastrophic failure as shown here :

[Sleepy]

That spacing is sized for the bake temperature (150C) expansion ...

" Metal bellows spaced every 130 feet took up the thermal expansion from the bake ... "

Ambient T swing will be smaller.

sidd

Maybe, but what will be considered as a safe range, all things considered?
Remember that the Swissmetro study recommended a cooling system despite beeing built into rock with much lower specs.
From one of my earlier comments:

Tin roofs here are specified for thermal expansions from -35°C up to +75°C, according to Swedish professionals.

The LIGO tubes are also made of 304L stainless steel (higher thermal expansion than steel).

Edit; Steel, as stated above using low estimates and a 40K T range vill require 7,500 joints capable of a 40 mm movement on each joint.

[Sigmetnow]

And you’re trying to tell me we can’t build a land-based tube of heavy steel that can withstand temperature extremes and a vacuum.   

http://www.bbc.com/news/science-environment-42969020

[DrTskoul]

https://en.m.wikipedia.org/wiki/Vactrain

A couple of hundred year old idea and problem ....

[TerryM]

I have no doubt that someone, somewhere, will build something that they will name using some variation of "Hyperloop".
It won't have much in common with Musk's "White Paper", but it will be some form of higher speed subway, possibly, but not likely, running in a partial vacuum.
The concept is older than our great grandparents, and the snappy new name may help with the financing.
Arguing against Hyperloop is futile simply because Hyperloop morphs into something new whenever the original is shown to be unrealistic.
Terry

[Rob Dekker]

OT. I'm sure that Sigmetnow would agree with me that today was an historic day for engineering.
The launch of the Falcon Heavy was amazing to watch, and the landing of two of the first stage rockets gave me shivers up my spine as an engineer.

And as a bonus we now have Elon's Tesla roadster in space, which will likely still be around long after humanity no longer exists.

Congrats to the 6000 people that made this happen, and big complement for Elon to for inspiring to go beyond our own limits and make engineering do magic.

Here is the whole thing, start to finish :



And none of this changes my opinions about Hyperloop being a really bad idea.

[Sleepy]

And you’re trying to tell me we can’t build a land-based tube of heavy steel that can withstand temperature extremes and a vacuum.   

No. You can absolutely build that.

Watched it live yesterday. The center core hit the drone ship in 300mph, according to Elon. That could be heard on the other feed from the control centre as well.
Grew up during the lunar missions and I had no shivers up my spine, this was a nice show though. Don't we (humanity) have better things to address?

Edit; here's that part from mission control. And another update, the center core hit the water 300 feet from the drone ship. Editing the video so hopefully everyone is able to watch this?

[Rob Dekker]

Grew up during the lunar missions and I had no shivers up my spine, this was a nice show though. Don't we (humanity) have better things to address?

Of course we do.

If the ultimate goal of SpaceX is to let people live on other planets like Mars, then of course we need to figure out first how to live SUSTAINABLY on our home planet.
Which means reaching the goal of living without fossil fuels (which Tesla is working hard on), stabilizing our climate, and our population.

This show by SpaceX today teaches us that we CAN reach out for hard to achieve goals.
And we should.
After all, if we don't reach out for them, we will never achieve them.

[Sleepy]

Sure Rob, I think Apollo showed that ability even more and we (humans) have not lost that.

But right now, our generation has choosen to fail on mitigating climate change. We should be reducing our emissions by 10-15% per year.
Sweden has 90% clean energy and still has to drop ~13% per year. EV's will be the first easy fix, then comes the tougher parts, that will be even harder to achieve.

[magnamentis]

I have no doubt that someone, somewhere, will build something that they will name using some variation of "Hyperloop".
It won't have much in common with Musk's "White Paper", but it will be some form of higher speed subway, possibly, but not likely, running in a partial vacuum.
The concept is older than our great grandparents, and the snappy new name may help with the financing.
Arguing against Hyperloop is futile simply because Hyperloop morphs into something new whenever the original is shown to be unrealistic.
Terry

as mentioned in another context i believe that all trials are ultimately helpful, no matter how big a fail and after alle the word: "hyper" "hype..." sounds great and has it's intended effects on most peoples mind while some people if they hear hyped names get all alarms firing.

last example in a long history (OT i know) is bitcoins, suddenly many people from all over the world felt like to ask me about my opinion and my reply was that the fact that it's in the news and they feel like asking means "hands off" too late, happens with all hypes and hyped stuff, mostly sooner but unfortunately sometimes way toooooo.... late to avoid desasters of various kinds.

[Sigmetnow]

...
Watched it live yesterday. The center core hit the drone ship in 300mph, according to Elon. That could be heard on the other feed from the control centre as well.
Grew up during the lunar missions and I had no shivers up my spine, this was a nice show though. Don't we (humanity) have better things to address?

Edit; here's that part from mission control. And another update, the center core hit the water 300 feet from the drone ship. Editing the video so hopefully everyone is able to watch this?

I knew you would focus in on the one bit of difficulty on the entire amazing, unprecedented accomplishment!  The center core ran out of igniter fluid for the landing burn, so only one out of three landing engines lit.  A one-engine landing burn, which they do use for certain missions, actually takes more fuel than a three-engine burn.  This is a problem they experienced before and is easily fixed!

None of the first stages were to be used again, anyway, because they are older versions of the Falcon 9 rocket.  Musk was quite happy that they brought back the very expensive titanium grid fins on the side boosters!  The side boosters themselves will likely be preserved, somewhere.

[Sleepy]

And you’re trying to tell me we can’t build a land-based tube of heavy steel that can withstand temperature extremes and a vacuum.   

No. You can absolutely build that.

I knew you would focus in on the one bit of difficulty on the entire amazing, unprecedented accomplishment!

You seem to know very much.

[Rob Dekker]

None of the first stages were to be used again, anyway, because they are older versions of the Falcon 9 rocket.  Musk was quite happy that they brought back the very expensive titanium grid fins on the side boosters!  The side boosters themselves will likely be preserved, somewhere.

These side boosters performed impeccable, and on multiple missions. Their simultaneous autonomous landings were an epic event yesterday, and a marvel of engineering accomplishment. Sad to see them retire.

[Sleepy]

I have no doubt that someone, somewhere, will build something that they will name using some variation of "Hyperloop".
It won't have much in common with Musk's "White Paper", but it will be some form of higher speed subway, possibly, but not likely, running in a partial vacuum.
The concept is older than our great grandparents, and the snappy new name may help with the financing.
Arguing against Hyperloop is futile simply because Hyperloop morphs into something new whenever the original is shown to be unrealistic.
Terry

Swedish SKF also uses the name Hyperloop for their version with speeds of up to 460km/h, that's even slower than the Swissmetro... If someone builds it, it will be far away from Elons white paper.

Found an interesting comment by Marcel Jufer about the 750 micron vacuum needed, who is one of the first and also oldest supporters of Swissmetro:

After reading through Musk’s hyperloop proposal, Jufer was intrigued yet concerned, especially about the vacuum pump system. Swissmetro is designed to run at about one-tenth atmospheric pressure, which is a great deal higher than hyperloop’s one-thousandth.

“At 7% of atmosphere, it’s very easy to produce that low pressure,” Jufer says. “It’s relatively cheap. But to go under this limit, you have to have a series of second pumps. The second pump is more complicated, more expensive, and probably it’s necessary to have three pumps in series to reach one-thousandth of the atmospheric pressure.”
Jufer, for his part, is open to collaborating with Musk. “Why not?”

The low-pressure of the hyperloop also presents a problem when loading passengers, Jufer adds. “You need to have some kind of airlock system at the extremity or in the stations for passengers.” he says. “Doing this, you introduce a relatively important amount of air. Not a large amount, but it’s at atmospheric pressure, which means if you introduce 1 cubic meter of air at atmospheric pressure, it means it’s equivalent to 1,000 cubic meters of air at low pressure. It’s a relatively important disturbance.”

Edit; placing the above comment by Marcel Jufer in quotes, also adding the fact that Rodolphe Nieth found support in Prof Marcel Jufer and a group of professors from the Swiss Federal Institute of Technology in Lausanne, in 1981.

[Sleepy]

Watched a TV program last night about HSR and the Shanghai Transrapid in particular. They mentioned that they had to develop a special body to cope with the shockwave when intersecting. Adding a short video, it sounds like they are lowering the speed just before the intersect.

Also adding two images from Marcel Jufer's paper from 2010, the following graph and table provides a comparison between rail-wheels, maglev by attraction and maglev by repulsion.

[TerryM]

Wow!
Assuming they were at speed, they'd have been at 430 kph and 350 kph. Their closing speed would have been 780 kpm or 485 mph.


The slower HSR would run from Los Angeles California to Las Vegas Nevada in just over one hour. Back in 2011 this train was transporting 82,000 passengers per day.


https://en.wikipedia.org/wiki/Shanghai_maglev_train

and

https://en.wikipedia.org/wiki/Shanghai%E2%80%93Hangzhou_high-speed_railway

These are not the newest designs. This maglev train has been running since 2004, and this HSR since 2010. North America is simply falling further and further behind the rest of the world.

Are we waiting for a technical fix that will leapfrog us over our competition, or will we simply delay attempting something we have neither the expertise, nor the financing to build?
Terry